These days, in order to achieve a print speed of 1 m/s and a print resolution of 1200 dpi, an inkjet recording device which is provided with a recording head for ejecting ink droplets drives the recording head by using a 100 kHz binary drive system which uses a drive frequency of 100 kHz (a pixel period of 10 us) and ejects zero or one ink droplet in one pixel period.
The 100 kHz binary drive system drives the recording head according to a drive waveform signal which includes, in one pixel period, an ejection pulse for ejecting one ink droplet and a cancel pulse for suppressing influence of reverberating vibration generated by the ejection pulse in a pressure chamber on a pressure wave therein.
FIG. 12i; shows a drive waveform signal in the 100 kHz binary drive system for ejecting ink droplets by a pull-push method, and FIG. 12ii; shows a pressure waveform in a pressure chamber generated by a pressure generation unit such as a piezoelectric element that applies pressure to ink according to the drive waveform signal. The voltage V0 represents a standby voltage in the pull-push method. In FIG. 12ii, time T1 and time T2 each indicate the time when an ink droplet is ejected (the time at which positive pressure becomes the maximum), the time T1 and the time T2 being the time after an ejection pulse P1 is applied and the time after an ejection P2 is applied, respectively. The ejection pulses P1 and P2 are each for ejecting an ink droplet. A solid line therein represents a pressure waveform in a case where a cancel pulse C1 is applied, and a dashed line therein represents a pressure waveform in a case where the cancel pulse C1 is not applied. In other words, as shown in FIG. 12ii, influence of reverberating vibration caused by the ejection pulse P1 is eased by the application of the cancel pulse C1, which reduces a positive pressure at time T2 to approximately the same as that at time T1. Accordingly, ejection speed of an ink droplet ejected on the basis of the ejection pulse P2 can be made the same as that of an ink droplet ejected on the basis of the ejection pulse P1.
Incidentally, the pixel period in the above case requires at least 4 AL when, as shown in FIG. 12i, the pulse width of each of the ejection pulse P1 and the cancel pulse C1 is AL (AL: Acoustic Length, i.e., a half period of a natural oscillation period of the pressure chamber), the cancel pulse C1 is applied after AL from the finishing time of the ejection pulse, and an interval after the application of the cancel pulse C1 is finished until the ejection pulse P2 in the next pixel period is applied is AL. Accordingly, in order to achieve the 100 kHz binary drive system (i.e., to make the drive frequency of the recording head reach 100 kHz), the natural oscillation period of the pressure chamber must be 5 us or less (the natural frequency must be 200 kHz or more).
The pulse width is the time from the start of falling of a pulse to the start of rising of the pulse or the time from the start of rising of a pulse to the start of falling of the pulse. For example, in the case shown in FIG. 13, each of a width T1 and a width T3 corresponds to the pulse width.
In consideration of the above, there is a method for driving a recording head by using a 50 kHz 2 dpd drive system which uses a frequency of 50 kHz (a pixel period of 20 us) and ejects zero to two ink droplets in one pixel period.
For example, as an inkjet recording device using the 2 dpd drive system, one is known which can efficiently and stably eject ink at high speed by synchronizing the pulse width of each ejection pulse with the natural oscillation period of a pressure chamber (refer to Patent Literature 1).